Support Range/Content-Range header when emitting response

[jakejohns]

SapiStreamEmitter (of zendframework/zend-diactoros) can emit a range of a file .

I'm thinking ResponseSender should maybe have some kind of conditional logic to do such a thing if the response Content-Range header is set on the Response it receives?

[pmjones]

That's a neat idea. If you want to send a PR, I'd be happy to review.